在ListView中延迟加载图像

我正在使用ListView来显示与这些图像相关的一些图像和标题。 我从互联网上获取图像。 有没有办法在文本显示时延迟加载图像，UI未锁定并且图像在下载时显示？

图像总数不固定。

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这是我创建的用于保存我的应用当前正在显示的图像。 请注意，这里使用的“Log”对象是我在Android内部的最终Log类中的自定义包装。

package com.wilson.android.library;

/*
 Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.
*/
import java.io.IOException;

public class DrawableManager {
    private final Map<String, Drawable> drawableMap;

    public DrawableManager() {
        drawableMap = new HashMap<String, Drawable>();
    }

    public Drawable fetchDrawable(String urlString) {
        if (drawableMap.containsKey(urlString)) {
            return drawableMap.get(urlString);
        }

        Log.d(this.getClass().getSimpleName(), "image url:" + urlString);
        try {
            InputStream is = fetch(urlString);
            Drawable drawable = Drawable.createFromStream(is, "src");


            if (drawable != null) {
                drawableMap.put(urlString, drawable);
                Log.d(this.getClass().getSimpleName(), "got a thumbnail drawable: " + drawable.getBounds() + ", "
                        + drawable.getIntrinsicHeight() + "," + drawable.getIntrinsicWidth() + ", "
                        + drawable.getMinimumHeight() + "," + drawable.getMinimumWidth());
            } else {
              Log.w(this.getClass().getSimpleName(), "could not get thumbnail");
            }

            return drawable;
        } catch (MalformedURLException e) {
            Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
            return null;
        } catch (IOException e) {
            Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
            return null;
        }
    }

    public void fetchDrawableOnThread(final String urlString, final ImageView imageView) {
        if (drawableMap.containsKey(urlString)) {
            imageView.setImageDrawable(drawableMap.get(urlString));
        }

        final Handler handler = new Handler() {
            @Override
            public void handleMessage(Message message) {
                imageView.setImageDrawable((Drawable) message.obj);
            }
        };

        Thread thread = new Thread() {
            @Override
            public void run() {
                //TODO : set imageView to a "pending" image
                Drawable drawable = fetchDrawable(urlString);
                Message message = handler.obtainMessage(1, drawable);
                handler.sendMessage(message);
            }
        };
        thread.start();
    }

    private InputStream fetch(String urlString) throws MalformedURLException, IOException {
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpGet request = new HttpGet(urlString);
        HttpResponse response = httpClient.execute(request);
        return response.getEntity().getContent();
    }
}

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我用图像做了一个懒惰列表（位于GitHub）的简单演示。 这可能对某人有所帮助。 它在后台线程中下载图像。 图像被缓存在SD卡和内存中。 缓存实现非常简单，对于演示就足够了。 我使用inSampleSize解码图像以减少内存消耗。 我也尝试正确处理回收的视图。

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我推荐开源仪器Universal Image Loader 。 它最初基于Fedor Vlasov的LazyList项目，自那时以来得到了极大的改进。

多线程图像加载

广泛调整ImageLoader配置的可能性（线程执行者，下载器，解码器，内存和磁盘缓存，显示图像选项等）

在内存和/或设备的文件系统（或SD卡）上进行图像缓存的可能性

可以“倾听”加载过程

可以使用单独的选项自定义每个显示图像调用

小部件支持

Android 2.0+支持

链接地址: http://www.djcxy.com/p/16627.html

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